The present invention relates generally to optical instruments for measuring eye aberrations in a patient and, more particularly, to apparatuses and methods for modifying the input beam entering the patient""s eye, patient corrective prescription verification, and binocular vision correction in ophthalmic wavefront measuring systems.
The eye is an optical system having several lens elements for focusing light rays representing images onto the retina within the eye. The sharpness of the images produced on the retina is a factor in determining the visual acuity of the eye. Imperfections within the lens and other components and material within the eye, however, may cause the light rays to deviate from the desired path. These deviations, referred to as aberrations, result in blurred images and decreased visual acuity. Hence, methods and apparatuses for measuring aberrations are used to aid in the correction of such problems.
One method of detecting aberrations introduced by the eye involves the determination of aberrations introduced into light rays when exiting from the eye. An input beam of light focused into the eye to a point on the retina is reflected or scattered back out of the eye as a wavefront, with the wavefront containing aberrations introduced by the eye. By determining the propagation direction of discrete portions (i.e., samples) of this wavefront, the aberrations introduced by the eye can be determined. The determined aberrations can then be used to produce corrective lenses and/or perform corrective procedures that restore visual acuity.
A general illustration of the generation of a wavefront is shown in FIG. 1. A wavefront 100 is generated by reflecting an input beam 102 off of the retina 104 of an eye 106. The input beam 102 focuses to a small spot 108 on the retina 104. The retina 104, acting as a diffuse reflector, reflects the input beam 102, resulting in the wavefront 100. Ideally, the wavefront 100 would be free of aberrations, as illustrated by the planar wavefront 110. However, aberrations introduced by the eye 106 as the wavefront 100 passes out of the eye 106 result in an imperfect wavefront, as illustrated by the aberrated wavefront 112. The wavefront 100 represents aberrations due to defocus, astigmatism, coma, spherical aberrations, and other irregularities. Measuring and correcting the aberrations allow the eye 106 to approach its full potential, i.e., the limits of visual resolution.
FIG. 2 is an illustration of a prior art ophthalmic wavefront measuring device for measuring aberrations within the wavefront 100 as illustrated in FIG. 1. A radiation source 114 (e.g., a laser) generates the input beam 102 which is routed to the eye 106 by a beam splitter 116. Typically, the input beam 102 generated by the radiation source 114 is substantially circular. The input beam 102 forms a spot 108 on the retina 104 of the eye 106. In an eye 106 free of imperfections, the spot 108 formed on the retina 104 is circular. Due to imperfections within the eye 106, the input beam 102 becomes aberrated, thereby resulting in the spot 108 formed on the retina 104 having a non-circular shape as illustrated in FIG. 2A. As will be discussed below, a retinal spot 108 with a non-circular shape affects adversely the determination of aberrations due to imperfections within the eye 106. The retina 104 then reflects the light from the spot 108 to create a wavefront 100 which is aberrated as it passes through the lens and other components and materials within the eye 106.
On the return path, the wavefront 100 passes through the beam splitter 116 toward a sensor 118. A quarter-wave plate 120 is positioned between the eye 106 and the beam splitter 116. The use of a quarter-wave plate 120 is a known technique for manipulating the polarization of the input beam 102 going into the eye 106 and the wavefront 100 emanating from the eye 106 so that the wavefront 100 is polarized in a direction perpendicular to the input beam 102, thereby enabling the wavefront 100 to pass through the beam splitter 116 toward the sensor 118. Additional lenses 122 are positioned between the eye 106 and the sensor 118 to image the plane of the pupil of the eye 106 onto the sensor 118 with a desired magnification. Information detected by the sensor 118 is then processed by a processor 124 to determine the aberrations of the wavefront 100 and determine a corrective prescription for the eye 106.
A typical sensor 118 includes a Hartman-Shack lenslet array 126 and an imaging device 128 containing an imaging plane 130 such as a charge coupled device (CCD) array. The lenslet array 126 samples the wavefront 100 and produces an array of spots 132 on the imaging plane 130, as illustrated in FIG. 2B, when the wavefront 100 passes through it. Each spot within the array of spots 132 is an image of the retinal spot 108. The relative positions of each spot within the array of spots 132 can be used to determine the aberrations of the wavefront 100.
Typically, the aberrations of the wavefront 100 are determined by determining an aberration for each sample of the wavefront 100 which are then combined. The determined aberrations are then used to calculate a corrective prescription for the eye 106.
The aberration of each sample of the wavefront 100 is determined by determining the centroid of a spot within the array of spots 132 and comparing the displacement between the centroid of the spot with a corresponding reference location, such as the location represented by reference spot 134. Since each spot within the array of spots 132 is an image of the retinal spot 108, if the retinal spot 108 is non-circular, as illustrated in FIG. 2A, each spot within the array of spots 132 will be non-circular, as illustrated in FIG. 2B.
Determining the centroid of a non-circular spot, however, is difficult, requiring significant processing time and power. Accordingly, since determining the centroid of the spots within the array of spots 132 is a prerequisite to determining the aberrations in the wavefront 100, and determining the centroid of a non-circular spot is difficult, non-circular spots on the imaging plane 130 affect adversely the speed and accuracy of computing aberrations. Therefore, apparatuses and methods for producing circular spots on the imaging plane 130 would be useful.
Another area for improvement is related to the ability of wavefront measuring devices to determine aberrations introduced by the eye 106 with a high degree of accuracy. This accuracy allows the determination of a corrective prescription for a patient that is precisely tailored to the patient""s visual needs. The precisely tailored corrective prescriptions, however, cannot be presented to the patient through a series of lenses as is traditionally done in determining corrective prescriptions at an eye doctor for example. This is due to the fact that each precisely tailored corrective prescription is so unique that it would be impossible to recreate the corrective prescription using a series of lenses without specially producing a lens having the corrective prescription. Accordingly, the patient is unable to determine if the corrective prescription determined by the wavefront measuring device satisfies the patient""s visual needs until prescription eye wear is produced (e.g., corrective lenses are ground or contact lenses are formed). Therefore, apparatuses and methods for allowing a patient to verify a corrective prescription prior to the production of corrective eye wear would be useful.
Yet another area for improvement is related to the dependancy of aberrations on binocular vision (i.e., viewing an object with both eyes at the same time). Prior art wavefront measuring devices such as the one depicted in FIG. 2 measure only one eye at a time. Accordingly, the affects of binocular vision on aberrations are not taken into consideration when developing corrective prescriptions and, therefore, the limits of visual resolution are not achieved in traditional wavefront aberration measuring devices. Therefore, wavefront measuring apparatuses and methods having binocular measurement capabilities would be useful.
The present invention discloses apparatuses and methods for improved aberration determination, corrective prescription verification, and binocular vision correction in wavefront measuring devices.
One aspect of the present invention is an input beam modifying apparatus and method for modifying an input beam into an eye for use with a wavefront measuring device to improve the measurement of aberrations. By modifying the input beam, the shape of an image formed on an imaging plane in a wavefront measuring device can be controlled to form a desired image, thereby facilitating calculations involved in determining aberrations. The input beam modifying apparatus comprises a sensor for sensing the image in the wavefront emanating from the eye in response to the input beam, an adaptive optical device for modifying the input beam, and a processor for receiving information from the sensor and adjusting the adaptive optical device to modify the input beam to produce a desired image at the sensor. The method for modifying the input beam includes sensing an image within a wavefront emanating from the eye in response to the input beam, and modifying the input beam to produce a desired image being sensed.
Another aspect of the present invention is a corrective prescription verification apparatus and method for use with a wavefront measuring device capable of generating information related to aberrations introduced by an eye. The corrective prescription verification apparatus and method enable a wavefront measuring device to present an image to a patient as it would appear if the patient were wearing corrective eye wear having a corrective prescription as determined by the wavefront measuring device. The corrective prescription verification apparatus includes a projector capable of emitting an image, an adaptive optical device capable of modifying the image emitted from the projector, and a processor capable of receiving the information related to aberrations introduced by the eye and adjusting the adaptive optical device to produce a corrected image. The corrective prescription verification method includes emitting the image of the scene and modifying the emitted image based on the information related to aberration introduced by the eye to produce a corrected image at the eye.
Yet another aspect of the present invention is a binocular wavefront measuring apparatus and method for determining aberrations in a pair of eyes at substantially the same time. The binocular wavefront measuring apparatus includes a first ophthalmic wavefront measuring device for measuring the aberrations introduced by a first eye of the pair of eyes and a second ophthalmic wavefront measuring device for measuring the aberrations introduced by a second eye of the pair of eyes. The binocular wavefront measuring method includes measuring the aberrations introduced by a first eye of the pair of eyes, measuring the aberrations introduced by a second eye of the pair of eyes, and determining a first corrective prescription for the first eye and a second corrective prescription for the second eye, wherein the aberrations of the first and second eyes are measured substantially simultaneously.